The present spray gun is of the hand-held air syphon operated type in which air is supplied to a control valve in a valve body hand-grip through an air fitting at the base of the grip. The trigger lever operated valve controls the flow of air through the valve body to a nozzle on the muzzle end of the gun, and this air is directed around a nozzle tip extending within an orifice in an air cap surrounding the nozzle tip whereby paint is aspirated through the nozzle from an adjacent container.
The nozzle assembly usually includes three machined parts, i.e., a nozzle, an adapter for attaching the nozzle to the valve body and a fluid inlet fitting connected to the fluid adapter to receive the paint container. These three parts and a fourth, the air cap, are usually constructed of metal and require a plurality of machining operations, rendering the nozzle assembly and air cap a major portion of the cost of the total spray gun.
Over and above the high cost of forming and machining the three nozzle assembly parts and the air cap, a major cause of poor paint atomization in spray guns is air leakage and the joints between the paint inlet fitting and the fluid adapter, between the fluid adapter and the nozzle, and between the adapter and the valve body, significantly increase the likelihood of this air leakage.
While it would be desirable to form the nozzle assembly parts and the air cap from molded plastic materials, it has not thus far been practical because the dimensional instability of plastics in the plastic molding operation does not satisfy the accuracy requirements for the nozzle assembly and air cap. For example, it is extremely important that the nozzle tip be perfectly concentric with the air cap orifice, and plastic moldings have not as yet achieved the required accuracy because of shrinkage and distortion. Furthermore, it is also necessary that the extent of axial projection of the nozzle tip from the air cap orifice be accurately controlled, and it was not heretofore thought possible that such axial control could be achieved with plastic parts.
One attempt to solve these problems is described in the co-pending application of John A. Gloviak and Tom G. Sprandel Ser. No. 727,065, filed Apr. 25, 1985, assigned to the assignee of the present application. In that application, a one-piece nozzle unit and nozzle tip is illustrated in which molding inaccuracies in the tip are corrected by the air cap. This solution, while suitable for many applications, is limited to cases of minimal nozzle tip distortion and relatively thin flexible nozzle tip walls.
It is a primary object of the present invention to ameliorate the problems noted above in conventional airoperated paint spray guns and to provide simplified plastic nozzle assembly and air cap parts.